This invention relates to methods and apparatus for efficiently moving print media to enable printing on both sides of the media. Printing on both sides of the media is known as duplex printing.
Duplex printing is a desirable feature in printing systems. The advantages of duplex printing include reducing the amount of paper required as compared to one-sided (simplex) printing, and generating print sets with layouts resembling that of professionally printed books. Conventional duplex printing devices employ complex media handling mechanisms. Typically, an extra tray is used for temporary storage of pages having printing on a first side. In an alternative approach, a second media path is provided to route a first printed page around the existing paper supply.
Similarly, duplex copying typically is accomplished by either one of two methods. In one method, first-side copies are stacked in a duplex tray. When a set of first-side copies is complete, the copies are fed out of the duplex tray and returned with an odd number of inversions along a duplex path to receive second-side imaging. In an alternative method, first-side copies are returned directly to receive second-side imaging without stacking.
Conventional duplexing devices tend to have long media paths and many parts. (Hereafter, the term xe2x80x9cpaperxe2x80x9d and xe2x80x9cmediaxe2x80x9d will be used interchangeably with the understanding that although paper is a common type of print media, that term is intended to include any other type of media for receiving printed information thereon.) A substantial challenge with devices having these complex paper paths is preventing paper jams and otherwise ensuring that the paper moves smoothly from one guide or roller to the next.
Also, as the paper path becomes more convoluted, there is an increased need for ensuring that the paper does not become skewed as it moves through the path. Skewing means a slight shifting or rotation of the sheet about an axis normal to the surface of the sheet. If a sheet becomes skewed as it moves between first-side and second-side printing, the second-side printing will not be evenly applied to the sheet. Accordingly, it is important that the paper path associated with a duplexing module be designed to ensure that skew does not occur. Preferably, such a non-skew paper path will be inexpensive to design and manufacture and require very little maintenance.
Certain media, such a photographic media, may suffer it is thereafter bent through too small a radius of curvature. For example, such small-radius bending of the sheet may cause the printed sheet to curl, which is undesirable. Nonetheless, there is oftentimes a need for duplex printing on photographic media. For instance, it may be desirable to print identifying information on the back of a printed, photo quality image. It is thus important to minimize the bending of the media (hence, protect against curl) as the photographic media is moved through the path for such duplex printing.
The present invention is directed to a duplexing module that is attachable to a printer that has a simplex media-handling system. The duplexing module is used in conjunction with the simplex system to carry out the print media handling (flipping) that is required for duplex printing.
The module of the present invention is intended for use with a printer that has a feed roller that is rotatable for moving print media toward the print source for printing on one side of the media. The rotation of the feed roller is reversible for thereafter moving the printed media away from the print source and into the adjacent duplexing module.
The duplexing module flips the print media and returns it to the feed roller with the non-printed side exposed for printing. In the present invention, the module includes a drive roller and an entry guide. The entry guide extends between a portion of the drive roller surface and a location adjacent to the feed roller. When the duplexing module is attached to the printer, the printer feed roller is driven to move the printed media sheet along the entry guide from where the sheet passes to the drive roller of the duplexing module.
The duplexing module also includes an exit guide that extends between the drive roller surface and a location adjacent to the feed roller, very near the location where the entry guide joins the feed roller. The print media (having one side printed) moves with the rotated drive roller until it reaches the exit guide. The printed side of the print media is directed against the feed roller of the printer so that the opposite side of the media is now ready for printing.
The method and apparatus of the present invention provides a very simple paper path through the duplexing module. To this end, only a single drive roller is employed for moving the paper away from and back to the feed roller of the printer. Thus, the manufacturing cost and complexity of the module is greatly reduced as compared to more complicated mechanisms for advancing the print media through the duplexing module. For example, the use of a single drive roller minimizes the number of required components (drive shaft, roller xe2x80x9ctiresxe2x80x9d etc.). Also, a single drive roller can be driven by the printer drive motor using a relatively simple drive connection.
Moreover, since the media is advanced through the duplexing module by a single roller, there is reduced likelihood of paper skew occurring. The media is substantially wrapped around the drive roller and rotates with the driver roller through about 270 degrees before being redirected from the drive roller back to the feed roller of the simplex printing system.
Another advantage of the use of a single drive roller in the duplexing module (as compared to the use of two or more drive rollers) is that there is reduced likelihood of the paper being stressed as it moves through the module. Specifically, in a system using two or more drive rollers the drive speeds of the rollers may not precisely match because of manufacturing tolerances (size of rollers, shafts, gears etc). Thus, if the second of a two-roller system is driven slightly faster than the first roller, the media will be pulled between the two rollers. The resultant tension in the media produces drag on the system that must be overcome with more torque applied to the roller. On the other hand, if the second of a two-roller system is driven slightly slower than the first roller, the media may become lose or even bunch up between the rollers.
The diameter of the drive roller of the duplexing module is selected to be relatively large. This reduces the radius that the print media is wrapped around. The use of a large-diameter roller reduces the torque that is required to move the media, especially relatively stiff media, such as card stock. Reduced torque increases the life of the drive motor. Thus, the use of a large diameter drive roller expands (for a given applied torque) the range of print media types (stiffness) that can be fed through the duplexing module.
Apparatus and methods for carrying out the invention are described in detail below. Other advantages and features of the present invention will become clear upon review of the following portions of this specification and the drawings.